The abnormal growth pattern of transformed or neoplastic cells is associated with characteristic surface properties. For example, transformed cells are more agglutinable by various plant lectins than their normal counterparts. This seems to reflect a topographical heterogeneity of lectin binding sites on the cell surface. Recently we have obtained evidence that microtubular proteins (MT) are instrumental in effecting the heterogeneous distribution of such binding sites in virus transformed cells, and transport proteins in phagocytic cells. The main thrust of the study has three basic aims: to obtain further evidence that microtubular proteins are determinants of surface heterogeneity, to explore further the relationship of MT to surface phenomena, particularly agglutinability, and to characterize biochemically the association between membranes and MT. The first objective will be approached by direct isolation and biochemical analysis of membrane internalized during phagocytosis with and without treatment with the alkaloids colchicine or vinblastine which specifically bind to or disrupt microtubules, and the second, by studies of hemagglutination of normal and transformed cells with and without alkaloids as a function of the cell cycle, trypsinization, and other parameters, and the third, by cell fractionation and analysis of membrane-associated microtubular (colchicine binding) proteins. These studies may serve as a basis for a new approach to the control of surface organization and hence of abnormal cell behavior.